Bluetooth: MGMT: fix zalloc-simple.cocci warnings

Use zeroing allocator rather than allocator followed by memset with 0

Generated by: scripts/coccinelle/api/alloc/zalloc-simple.cocci

Signed-off-by: Yihao Han <hanyihao@vivo.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>